VII] INSECTICIDES AND FUNGICIDES 65 



with sodium bicarbonate, add 4-5 grams in excess, and then sufficient 25% ammonium 

 chlorid solution to dissolve the precipitated copper. Dilute somewhat and titrate 

 as directed under 3 (C) . A correction must be applied for the amount of iodin solu- 

 tion necessary to produce a blue color with starch in the presence of copper (using 

 an equivalent weight of copper sulphate) . The corrected number of cc . of the stand- 

 ard iodin solution used represents directly the per cent of arsenious oxid (AsiOi) 

 in the sample. 



Method II. 



8 CM. Smith Method,^ Modified— Tentative. 



Proceed as directed in 7, using dilute sulphuric acid (1 to 4) instead of dilute 

 hydrochloric. The solution in this case may be heated to boiling. 



SODIUM ACETATE-SOLUBLE ARSENIOUS OXID.<— TENTATIVE. 



9 REAGENTS. 



(a) Sodium acetate solution .—Vrepare a solution containing 12.5 grams of the 

 crystallized salt (CHaCOONaSHzO) in each 25 cc. 

 The other reagents are described under 3. 



10 DETERMINATION. 



Place 1 gram of the sample in a 100 cc. flask and boil for 5 minutes with 25 cc. of 

 the sodium acetate. Dilute to the mark, shake, and pass through a dry filter 

 paper. Titrate an aliquot of this filtrate as directed under 3 (C). Calculate the 

 amount of arsenious oxid (AS2O3) present and express the result as per cent of 

 sodium acetate-soluble arsenious oxid. 



WATER-SOLUBLE ARSENIOUS OXID.— TENTATIVE. 



11 REAGENTS. 



Described under 3. 



12 DETERMINATION. 



To 1 gram of the sample in a liter Florence flask add 1 liter of recently boiled water 

 which has been cooled to exactly 32°C. Stopper the flask and place in a water 

 bath kept at 32°C. by means of a thermostat. Digest for 24 hours, shaking hourly 

 for 8 hours during this period. Filter through a dry filter and titrate 250 cc. of the 

 filtrate as directed under 3 (C) . Correct for the amount of the standard iodin neces- 

 sary to produce the same color, using the same reagents and volume. Calculate 

 the amount of arsenious oxid (AS2O3) present and express the result as per cent of 

 water-soluble arsenious oxid. 



TOTAL COPPER OXID. 



13 Electrolytic Method.— Official. 



Treat 2 grams of the sample in a beaker with 100 cc. of water and about 2 grams 

 of sodium hydroxid and boil thoroughly until all the copper is precipitated as cu- 

 prous oxid. Filter, wash well with hot water, dissolve the precipitate in hot dilute 

 nitric acid, cool, transfer to a 250 cc. graduated flask and dilute to the mark. (1) 

 Use 50-100 cc. of this solution for the electrolytic determination of copper as directed 

 under VIII, 33 and calculate to per cent cupric oxid; or, (2) Electrolyze the aliquot in 

 a weighed 150 cc. platinum dish, using a rotating spiral anode and a current of about 



